The present invention relates to a glia activating factor, a novel polypeptide, which is obtained from glioma cell culture solution and exhibits growth promoting activity against glial cells, fibroblasts and the like, a DNA coding for the glia activating factor, and a recombinant DNA for the preparation of the glia activating factor.
Various growth factors have been discovered, studied and utilized [Cellular & Molecular Biology, edited by The Japanese Tissue Culture Association, Asakura Shoten (1987)]. Such cell growth factors include epidermal growth factor (EGF), platelet-derived growth factor (PDGF), acidic fibroblast growth factor (aFGF) and basic fibroblast growth factor (bFGF). All of these factors have been isolated based upon growth promotion of fibroblast cells. However, these factors have also been found to display widely ranging activity and poor specificity. Accordingly, recent attempts have been made to search for growth factors specifically acting on functionally differentiated cells. As a result, growth factors such as keratinocyte growth factor (KGF) and hepatocyte growth factor (HGF) have been isolated, thus creating the possibility that these factors could be used to treat diseases vulnerable to their specific action spectra.
Encephalopathy of old age, particularly dementia, has been found to result from known disorders, such as injury-provoked cerebral nerve cell death, and from unknown disorders. Because cerebral nerve cells cease to proliferate immediately after birth and thereafter gradually decrease in number, there is no natural mechanism by which to repair damaged cerebral nerve cell or add new cerebral nerve cells at any significant rate. Thus, restoration of cerebral nerve cell activity requires artificial stimuli.
Glial cells, classified according to their form and function as either Type I or II astrocyte, or oligodendrocyte, surround and support the survival of cerebral nerve cells. The activation of these glial cells results in the activation and retention of the cerebral nerve cells. Such activation and retention is an important measure for improvement in an encephalopathologic condition. Despite extensive research into the identification of the neurotrophic factor released by glial cells, no decisive factor has been discovered as yet. Accordingly, research has focused upon the activation of the glial cells and the growth factors acting on those glial cells.
As described above, the identification and isolation of growth factors acting on the glial cells have been researched, in order to exploit their ability to activate cerebral nerve cells, and PDGF and FGF have been known to exhibit growth promoting activity also against the glial cells. However, the specificity of these factors is so poor that they exhibit strong strong growth promoting activity against other types of cells. Accordingly, they have not been able to be satisfactorily used as drugs. In sum, the prior art had not successfully identified a factor which strongly and specifically activated glial cells, and thus did not provide a drug capable of treating encephalopathy.